Field of the Invention
The present disclosure relates to a control of an image forming apparatus, and in particular relates to a control of an electrophotographic image forming apparatus.
Description of the Related Art
Electrophotographic image forming apparatuses have been widely used. The electrophotographic image forming apparatuses each perform a printing process including the steps of rotating an image carrier while uniformly charging the image carrier, exposing the image carrier to form an electrostatic latent image, applying toner to the electrostatic latent image on the image carrier, transferring a toner image on the image carrier to an object on which printing is to be performed, removing the toner remaining on the image carrier using a cleaning blade after transfer of the toner image, and applying lubricant to the image carrier.
A method of applying the lubricant on the image carrier uses for example, a lubricant application mechanism and a toner additive. The lubricant application mechanism is configured so that a brush is rotated and made contact with a solid lubricant called lubricant bar, and lubricant scraped by the brush is supplied to a surface of the image carrier. In the toner additive, a lubricant is added to toner, the toner forms a toner image, and the lubricant is supplied to the surface of the image carrier through the toner.
The lubricant applied over the image carrier is reduced due to accumulation of the toner, toner additive, or the like on the cleaning blade. That is, the amount of reduction in lubricant on the image carrier varies depending on the amount of toner accumulated on the cleaning blade. In a portion having a large amount of toner, the amount of reduction in lubricant on the image carrier is increased, and in a portion having a small amount of toner, the amount of reduction in lubricant on the image carrier is reduced. Therefore, even if the lubricant is uniformly applied over the image carrier, the amount of lubricant may be not uniform on the image carrier.
This may cause an uneven image (noise). FIGS. 13A and 13B are exemplary diagrams illustrating image unevenness. Let us assume that an image pattern 130 having a black center region 131 is continuously printed. In this case, the amount of reduction in lubricant on the image carrier is increased in a region corresponding to the center region 131, and is reduced in the other regions, on the image carrier. Adhesion between the image carrier and toner varies depending on the amount of lubricant, and even if uniform image pattern (whole half tone) is printed, unevenness is caused between the regions 136 and 137, as shown in an image 135. In order to prevent generation of image unevenness, it is important to make the lubricant on the image carrier uniform regardless of an image pattern.
As for a technique for inhibiting image unevenness, for example, JP 2009-69582 A discloses an image forming apparatus for “always making the amount of lubricant on an image carrier constant”. JP 2010-169793A discloses an image forming apparatus for “maintaining a uniform amount of lubricant applied to a surface of an image carrier regardless of an image output”.
With reference to FIGS. 14A to 14C, an example of a method of inhibiting the image unevenness will be described. FIGS. 14A to 14C are graphs each illustrating a relationship between the rotation rate of a lubricant application member and the amount of lubricant on the image carrier. Hereinafter, a toner region on the image carrier is also referred to as “image portion”. A region on the image carrier to which toner is not applied is also referred to as “background portion”.
Lower curves in graphs of FIGS. 14A to 14C each indicate change in amount of lubricant with respect to the rotation rate of the lubricant application member when the image portion is continued. Upper curves in the graphs of FIGS. 14A to 14C each indicate change in amount of lubricant with respect to the rotation rate of the lubricant application member when the background portion is continued. For example, as indicated in the graph of FIG. 14A, when the rotation rate of the lubricant application member is set to “A1”, there is a difference “C1−B1” in amount of lubricant between the background portion and the image portion. This difference exceeds an allowable width W not causing the image unevenness, so that the image unevenness is caused.
An example of the method of inhibiting the image unevenness includes a method of reducing the rotation rate of the lubricant application member to reduce a difference in amount of lubricant between the background portion and the image portion, from “C1−B1” to “C2−B2”, as shown in the graph of FIG. 14B. With this method, a difference in amount of lubricant is within the allowable width W, and the image unevenness is not generated. However, with this method, the amount of lubricant on the image carrier is lower than a threshold Th, and so-called toner fixation on the photoreceptor, that is, toner fixation on a photoreceptor is generated.
Another example of the method of inhibiting image unevenness includes a method of increasing the rotation rate of the lubricant application member, to reduce a difference in amount of lubricant between the background portion and the image portion, from “C1−B1” to “C3−B3”, as shown in the graph of FIG. 14C. With this method, a difference in amount of lubricant is within the allowable width W, and the image unevenness is not generated. In this case, the amount of lubricant on the image carrier exceeds the threshold Th, and the toner fixation on a photoreceptor is not generated.
The image forming apparatuses disclosed in JP 2009-69582 A and JP 2010-169793 A inhibit the image unevenness using such a method. More specifically, the image forming apparatus disclosed in JP 2009-69582 A divides an area on the image carrier into a plurality of regions, calculates toner consumption on the image carrier, for each region, and applies lubricant when the toner consumption has a value not less than a predetermined threshold in any region. Similarly, the image forming apparatus disclosed in JP 2010-169793 A divides an image area into regions in a main scanning direction, detects toner consumption in each region, and increases an amount of the lubricant applied, when the toner consumption has a value not less than a certain level, in some of the regions.
However, even if the toner consumption has a value not less than the certain level, unevenness in application may be not generated without increasing the amount of the lubricant applied, depending on a relationship with peripheral regions. In this case, the lubricant is wasted.